Detection of wood properties using a heating and cooling method - II. Detection of knots on wood surfaces

It can be postulated that the temperature on wood surfaces during heating o r successive heating and cooling processes is affected by wood density. In general, the density of knots is different from its surrounding area. It mi ght be possible to detect knots on the wood surface by measurement of the d istribution of its temperature. After heating of sugi boards having exposed knots of about 20 mm diameter, in the temperature range of 135 degrees C a nd 270 degrees C for 30 seconds, the distribution of temperature on the boa rd surface was measured during cooling at 20 degrees C under the condition of natural convection. In the case of heating at 270 degrees C and cooling at 20 degrees C for 16 seconds, the existence of a knot on the board surface was easily distinguis hed as the temperature on the surface of the knot and surrounding area were shown 54 degrees C and 72 degrees C respectively. But the temperature diff erence between the knot and the surrounding area became less and the detect ion of knots on the wood surface more difficult with decreasing heating tem perature and increasing cooling time.